Coating of tubing



Dec. 24, 1968 J, F. CLARKE 3,417,453

coATING oF TUBING Filed 001'.. 15, 1965 United States Patent O 3,417,453 CATING F TUlliNG John F. Clarke, Attleboro, Mass., assignor to Texas Instruments Incorporated, Dailas, Tex., a corporation of Delaware Filed Oct. 13, 1965, Ser. No. 495,502 4 Claims. (Cl. 29-460) ABSTRACT OF THE DISCLOSURE A metal strip is drawn through a curling die to form a tube, the adjacent edges of which are welded beyond the die. The tube then moves through heating means in a heating chamber and iinally through a finishing die. A hollow mandrel extends through the curling die into the welded tube beyond the heating zone where the mandrel has outlets and a tube plug therebeyond. A gas or vapor which is decomposable by heating is introduced into the moving tube through the mandrel and its outlets. Because of the plug the gas or vapor back-flushes through the advancing tube Within its heated zone and out through its open portion at the curling die. It escapes through a chamber having a valve-controlled vapor outlet to control the rate of ow. The outside of the tube in the heating chamber may also be subjected to `a neutral, deoxidizing, or a decomposa'ble gas or vapor, the iiow of which through the heating chamber is controlled by a valve-.controlled chamber outlet. The temperature established in the heating zone is sufficient to decompose the back-flushing vapor or gas, which condenses on the inside of the tube as it cools in its movement away from the heating zone. If a decomposable vapor or gas is used in the heating chamber, there will be formed an outside deposit on the tube.

proved tubing having complete coating on its inside suryface and, if desired, also on its outside surface; and the provision of a low-cost continuous .process which is particularly applicable to the manufacture of improved welded metal tubing having a continuous inside metal coating, and, if desired, also a continuous outside metal coating. Other objects and features will be in part apparent and in part pointed out hereinafter.

Satisfactory commercial methods for continuously applying a metal coating to the inside of a metal tube have not fbeen developed. Batch processes have been used; for example, by the extrusion of two coaxial tubes, followed by drawing to finished size. This, however, results in production in limited lengths and is expensive. An indirect continuous method exists, whereby a metal strip is first clad to a second metal strip, both then being bent into tubular form `and seam-welded. This has the disadvantage that continuity of the inside facing of the tubing becomes impossible and can be approximated only by the use of very elaborate seaming techniques. By means of the present invention, a chemical vapor deposition of material is effected in a continuous process to overcome the abovementioned problems.

The invention accordingly comprises the methods, constructions and products hereinafter described, the scope of the invention being indicated in the following claims.

In the accompanying drawings, illustrating one form of the invention:

FIG. 1 is a diagrammatic view illustrating the process and apparatus for producing the tubing; and

3,417,453 Patented Dec. 24, 1968 FIG. 2 is an enlarged axial section of certain parts shown at the left of FIG. l.

Referring now to the drawings, there is illustrated at numeral 1 a housing divided by a wall 3 into gas chambers 5 and 7. At numeral 9 is an inlet opening means into the chamber 5 for admitting a moving metal strip 11 from which desired metal tubing is to fbe formed. This opening means also admits a hollow mandrel or injection device which carries a chemical vapor to be described.

Mounted on the wall 3 is a curling die 17 for receiving the moving strip 11 and converting it to the desired tubular form. This form may be circular, elliptical or the like, the circular form being illustrated. The curling die 17 is shaped to bring together the two edges 19 of the strip as the tubular form leaves the die and moves through the chamber 7, as shown.

At numeral 21 is diagramatically illustrated welding means for continuous fusion-welding of the edges 19 as the latter leave the die 17 to complete the desired tube, which is numbered 23. The station for the welder 21 is near the outlet of die 17, as illustrated.

On a wall 25 of the chamber 7 is located a drawing or finishing die 27. This is related substantially coaxially with the curling die 17. The hollow mandrel 15 extends through the die 17 and spacedly within the tube 23 (see FIG. 2). At its end near the die 27 the mandrel 15 has a constriction 29 and an enclosing head 33. Openings 31 are provided through the construction 29. The head 33 closes the end of the hollow mandrel 15 and substantially forms a darn in the tube 23 where it is being finished in the die 27 At numeral 35 are shown draw rolls for pulling the tube 23 and the strip 11.

At numeral 37 is diagrammatically shown an electrical induction heating coil, located between the -gas outlet openings 31 and the welding station 20. This coil 37 surrounds the tube 23 for providing a heating region or zone 3S for heating the tube in its welded condition as it advances from the welding station to the die 27.

At numeral 39 is shown `an inlet for a suitable atmosphere of gas or vapor to be carried in the chamber 7. At numeral 41 is a valved outlet for controlling the flow of this atmosphere through the chamber 7. The nature of the gas to be employed in the chamber 7 will be discussed below.

At numeral 43 is a valved outlet from the chamber 5 to control the flow of vapor therefrom, as will appear. The inlet end 45 of the hollow mandrel 15 is connected by suitable means with a supply of vapor for chemical vapor deposition. This vapor is forced'through the mandrel 15 and escapes into the welded tube 23 through the openings 31. Because the mandrel head 33 acts substantially as a plug in the die 27, the vapor which escapes from the openings 31 flushes back through the welded tube 23, through the heated region 38, escaping through the curling die 17 into the chamber 5. The annular space between the mandrel 15 and the tube 23 is enough to accommodate a substantial flow through the welded tube 23. The vapor flow is shown by the darts in the drawings. The control at the outlet 43 determines the rate at which the vapor flows.

Operation is as follows:

A strip 11 of the proper dimensions and composition for the tubing desired is fed through the chamber 5 and formed into tubular shape by the die 17, welding occurring at the location lof the welder 21. The resulting welded tube 23 in the second chamber 7 has its outside exposed to whatever gas is carried in chamber 7. This gas may form a neutral atmosphere, such as, for example, argon, or it may be an oxide-reducing gas if it is desired to remove any oxide that may be on the outside of the tube 23, if metallic. In the latter case the gas may be hydrogen, cracked ammonia or the like. The use of such atmospheres may be omitted under some circumstances.

The vapor which is fed through the mandrel and which ushes back around it within the welded tube 23 passes through the heating zone 38 effected by the heat- 5 ing coils 37. The temperature established in this zone `by the coils 37 is that which will decompose this vapor into the material which is to be vapor-deposited on the inside of the tubing and the gaseous decomposition products. Undeposited gaseous decomposition products are forced back through the tube 23, out of the die 17 and into the chamber 5, from which they escape through the controlled outlet 43. The decomposition product or material deposited on the inside of tube 23 covers its linear weld as well as its other inside portions. The unused vapor which is flushed back and out of the chamber 5 through outlet 43 may be purified and recycled, as desired.

If it is desired to apply a coating on the outside of the tube 23, as well as on its inside, then an atmosphere is 20 carried in chamber 7 which is of the proper composition for chemical vapor decomposition in the heating zone of the coils 37. This will form a deposit on the outside of the tube. If it is to form the same coating as on the inside of the tube, then the same type of vapor is provided in 2 the chamber 7 as enters through the hollow mandrel 15. If a different exterior coating is desired, then another appropriate vapor for chemical vapor deposit will be carried in chamber 7.

Examples of vapors that may be used for chemical vapor deposition at appropriate temperatures on the substrate materials of which the welded tube 23 may be composed are as follows, the transforming equations being given, said equations showing the reaction temperature to be maintained in region 3S for deposition:

200 o. linternas 2Ai+3Hy+eCiu to deposit aluminum on steel or copper tube.

s o. Mom-93H2 MO+GHF to deposit molybdenum on copper tube.

to deposit columbium on a variety of metals for the tube.

500 to 750 C.

WFG-F3112 W+0HF to deposit tungsten on a copper or nickel tube.

to deposit tungsten carbide on a steel tube.

VII

to deposit boron nitride on a molybdenum or tantalum tube.

The above examples are not to be taken as limiting,

. inasmuch as there are many other known chemical vapor transformations that occur and which may be used in connection with an apropriate substrate (tube 23). It will be understood that the principles of the invention are applicable to the use of nonmetals for the tubing and lining.

In view 0f the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

As many changes could be made in the above methods, constructions and products without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. The method of manufacturing an internally lined metal tube, comprising drawing a metal strip through a curling die through which extends a vapor injection device continuously to bring together the edges of the strip around said injection device, continuously Welding the edges together at a welding station to form a moving welded tube having an open end at the curling die, introducing into the welded moving tube through said injection device a decomposable vapor to flow through the tube as welded to and out ot` said open end, said vapor being decomposable at an elevated temperature, and heating the welded tube in a Zone where the vapor flows through it to the decomposition temperature of the vapor to form a metal deposit on the inside of the tube.

2. The method according to claim 1, including the step of flowing a similarly decomposable vapor around the tube in said zone to form a metal deposit on the outside of the tube.

3. The method of manufacturing a metal tube, comprising moving a metal strip through a curling die to bring together its edges, welding said edges after they leave the curling die to form a welded tube, passing the `welded tube through a heating zone, said tube moving around an injection device extending therein through the curling die, said injection device providing an outlet in the tube beyond the heating zone and a plug beyond the outlet, introducing a vapor through said injection device for movement from the outlet and through the welded tube past said heating zone and toward the curling die, said vapor being of a nature for decomposition within a certain temperature range into a metallic vapor and gaseous products of decomposition, and maintaining said heating zone in said temperature range, whereby the metallic vapor forms as a metallic liner in the moving welded tube and said products of decomposition escape therefrom.

4. The method according to claim 3, including the step of passing around the tube in the heating zone a vapor of similar nature.

References Cited UNITED STATES PATENTS 2,982,312 5/1961 Caplan et al. 29-429 X 3,007,810 11/1961 Hobrock 117-97 X 3,031,338 4/1962 Bourdeau 117-97 FOREIGN PATENTS 822,073 10/ 1959 Great Britain.

r CHARLIE T. MOON, Primary Examiner.

C. E. HALL, Assistant Examiner.

U.S. Cl. XR. 

